1. Field of the Invention
The present invention relates to a polymer dispersed liquid crystal display device and a method of manufacturing the same, and more particularly, to a polymer dispersed liquid crystal display device capable of displaying a high-quality image and a method of manufacturing the same.
2. Description of the Related Art
A polymer dispersed liquid crystal display device is formed such that a composite film consisting of a polymer resin and a liquid crystal and formed by dispersing the polymer and the liquid crystal is arranged between a pair of transparent substrates having transparent electrodes formed thereon. This composite film has a structure obtained by confining a liquid crystal (domains of a liquid crystal) in each space of a polymer resin layer having a sponge-like sectional structure. Note that, as the liquid crystal, a nematic liquid crystal having positive dielectric anisotropy is generally used.
The polymer dispersed liquid crystal display device is driven by applying a voltage across the electrodes of both the substrates. In a state wherein no voltage is applied, the molecules of the liquid crystal of the composite film are pointed in various directions. In this state, light transmitted through the composite film is scattered by the light scattering effect of the interface between the liquid crystal and the polymer and the liquid crystal domains. When a voltage exceeding a voltage having a predetermined threshold value is applied across the electrodes, the molecules of the liquid crystal of the composite film are aligned in a direction substantially perpendicular to the substrate surfaces. In this state, light is transmitted through the composite film under almost no influence of the light scattering effect. In other words, the polymer dispersed liquid crystal display device controls scattering and transmission of light to display an image.
The polymer dispersed liquid crystal display device is generally formed by the following processes.
(1) A pair of transparent substrates are bonded to each other through a frame-like seal member.
(2) A solution mixture of a liquid crystal and a polymerization material which causes a polymerization reaction with light is sealed in an area surrounded by the pair of substrates and the seal member. (3) Light (ultraviolet ray) is radiated on the polymerization material of the solution mixture to polymerize the polymerization material, thereby forming a composite film. When this manufacturing method is used, if the gap between both the substrates is ununiformed, the thickness of the formed composite film become ununiformed, and an ununiformed display occurs.
For this reason, in the polymer dispersed liquid crystal display device, as in a TN type liquid crystal display device or the like, when a pair of transparent substrates are connected to each other through a seal member, spacers are arranged at various positions between the pair of transparent substrates to make the gap between the substrates uniform.
As the spacers, grains or short fibers consisting of glass, a hard resin, or the like are conventionally used. The spacers include transparent spacers and opaque black spacers.
In a polymer dispersed liquid crystal display device in which the gap between substrates is uniformed by transparent spacers, even in a state wherein no voltage is applied across the opposing electrodes (a state wherein the molecules of the liquid crystal of a composite film are pointed in various directions, and a dark display is performed), light transmitted through the spacer portion is transmitted through the spacers without being scattered. For this reason, an observer sees a display image as if bright points formed by the light transmitted through the space portion are present at various positions of the display image.
In a polymer dispersed liquid crystal display device in which the gap between substrates is uniformed using black spacers, even in a voltage application state (a state wherein the molecules of the liquid crystal of a composite film are uniformly aligned in a direction perpendicular to the major surfaces of the transparent substrate, and a bright display is performed), light transmitted through a spacer portion is absorbed by the spacers. For this reason, an observer sees a display image as if black points formed by the shadows of the spacers are present at various positions in the display image.
For this reason, in a conventional polymer dispersed liquid crystal display device, the bright or black points described above are present at various positions in the display image, and the quality of the display image is poor. In particular, when the conventional polymer dispersed liquid crystal display device is used as the display section of a liquid crystal projector in which the display image of the liquid crystal display device is enlarged by a lens and projected on a screen, the bright or black points become conspicuous, and the display quality is more degraded. In addition, the conventional polymer dispersed liquid crystal display device cannot obtain a high contrast.